The present invention relates to an electrophotographic system, which has a member with a surface layer and also may include a base layer. The surface layer is prepared from a surface layer composition, which includes a fluoroelastomer, and a boron nitride filler coupled with a silane.
In a typical electrostatographic reproducing apparatus, a light image of an original to be copied is recorded in the form of an electrostatic latent image upon a photosensitive member and the latent image is subsequently rendered visible by the application of electroscopic thermoplastic resin particles which are commonly referred to as toner. The visible toner image is then in a loose powdered form and can be easily disturbed or destroyed. The toner image is usually fixed or fused upon a support which may be the photosensitive member itself or other support sheet such as plain paper.
The use of thermal energy for fixing toner images onto a support member is well known. In order to fuse electroscopic toner material onto a support surface permanently by heat, it is necessary to elevate the temperature of the toner material to a point at which the constituents of the toner material coalesce and become tacky. This heating causes the toner to flow to some extent into the fibers or pores of the support member. Thereafter, as the toner material cools, solidification of the toner material causes the toner material to be firmly bonded to the support.
Typically, the thermoplastic resin particles are fused to the substrate by heating to a temperature of between about 75xc2x0 C. to about 160xc2x0 C. or higher depending upon the softening range of the particular resin used in the toner. It is undesirable, however, to raise the temperature of the substrate substantially higher than about 200xc2x0 C. because of the tendency of the substrate to discolor at such at elevated temperatures particularly when the substrate is paper.
Several approaches to thermal fusing of electroscopic toner images have been described in the prior art. These methods include providing the application of heat and pressure substantially concurrently by various means: a roll pair maintained in pressure contact; a belt member in pressure contact with a roll, and the like. Heat may be applied by heating one or both of the rolls, plate members or belt members. The fusing of the toner particles takes place when the proper combination of heat, pressure, and contact time are provided. The balancing of these parameters to bring about the fusing of the toner particles is well known in the art, and they can be adjusted to suit particular machines or process conditions.
During operation of a fusing system in which heat is applied to cause thermal fusing of the toner particles onto a support, both the toner image and the support are passed through a nip formed between the roll pair, or plate or belt members. The concurrent transfer of heat and the application of pressure in the nip effects the fusing of the toner image onto the support. It is important in the fusing process that no offset of the toner particles from the support to the fuser member takes place during normal operations. Toner particles offset onto the fuser member may subsequently transfer to other parts of the machine or onto the support in subsequent copying cycles, thus increasing the background or interfering with the material being copied there. The so called xe2x80x9chot offsetxe2x80x9d occurs when a splitting of the molten toner takes place during the fusing operation with a portion remaining on the fuser member. The hot offset temperature or degradation of the hot offset temperature is a measure of the release property of the fuser roll, and accordingly it is desired to provide a fusing surface which has a low surface energy to provide the necessary release. To insure and maintain good release properties of the fuser roll, it has become customary to apply release agents to the fuser members to insure that the toner is completely released from the fuser roll during the fusing operation. Typically, these materials are applied as thin films of, for example, silicone oils to prevent toner offset.
Some recent developments in fuser members, release agents and fusing systems are described in U.S. Pat. Nos. 4,257,699 and 4,264,181 to Lentz and U.S. Pat. No. 4,272,179 to Seanor. These patents describe fuser members and methods of fusing thermoplastic resin toner images to a substrate where a polymeric release agent having functional groups is applied to the surface of the fuser member. The fuser member comprises a base member having an elastomeric surface with a metal containing filler therein which has been cured with a nucleophilic addition curing agent. Examples of such a fuser member is an aluminum base member with a poly(vinylidenefluoride-hexafluoropropylene) copolymer cured with bisphenol curing agent having lead oxide filler dispersed therein and utilizing a mercapto functional polyorganosiloxane oil as a release agent. In those fusing processes, the polymeric release agents have functional groups (also designated as chemically reactive functional groups) which interact with the metal containing filler dispersed in the elastomer or resinous material of the fuser member surface to form a thermally stable film which releases thermoplastic resin toner and which prevents the thermoplastic resin toner from contacting the elastomer material itself. The metal oxide, metal salt, metal alloy, or other suitable metal compound filler dispersed in the elastomer or resin upon the fuser member surface or the elastomer or resin therein interacts with the functional groups of the polymeric release agent. Preferably, the metal containing filler materials do not cause degradation of or have any adverse effect upon the polymeric release agent having functional groups. Because of this reaction between the elastomer having a metal containing filler and the polymeric release agent having functional groups, excellent release and the production of high quality copies are obtained even at high rates of speed of electrostatographic reproducing machines.
In electrophotographic fuser systems, fuser roller overcoats are made with layers of polydimethylsiloxane (xe2x80x9cPDMSxe2x80x9d) elastomers, fluorocarbon resins, and fluorocarbon elastomers. PDMS elastomers have low surface energy and relatively low mechanical strength, but is adequately flexible and elastic and can produce high quality fused images. After a period of use, however, the self-release property of the roller degrades and offset begins to occur. Application of a PDMS oil during use enhances the release property of the fuser roller surface but shortens roller life due to oil swelling. Fluorocarbon resins like polytetrafluoroethylene (xe2x80x9cPTFExe2x80x9d) have good release properties but less flexibility and elasticity than PDMS elastomers. Fluorocarbon elastomers, such as Viton(trademark) and Fluorel(trademark), are tough, flexible, resistant to high temperatures, durable and do not swell, but they have relatively high surface energy and poor thermal conductivity.
Particulate inorganic fillers have been added to fluorocarbon elastomers and silicone elastomers to increase mechanical strength and thermal conductivity. High thermal conductivity is an advantage because heat needs to be efficiently and quickly transmitted to the toner from the outer surface of the fuser roller to fuse the toners and yield the desired toner images. However, incorporation of inorganic materials to improve thermal conductivity has a major drawback: it increases the surface energy of fuser roller surface and also increases the interaction of the filler with the toner and receiver. After a period of use, the toner release properties of the roller degrade and toner offset begins to occur due to roller wear and weak interaction between the filler and the polymer matrix. It would be desirable to provide a fuser member having a fluorocarbon elastomer overcoat layer containing thermally conductive inorganic fillers, but which still has good toner release property. In addition, the outer surface of the fuser member should be compatible with the functionalized polymeric release agent employed during the fixing process.
Fuser members of fluorocarbon elastomer containing inorganic fillers are disclosed, for example, in U.S. Pat. No. 5,595,823 to Chen et al., which describes fuser rollers having a surface layer comprising fluorocarbon elastomer and aluminum oxide fillers. These fillers are not treated and are prone to high reactivity with the toner and charge control agents and this, too, is undesirable.
U.S. Pat. No. 5,017,432 to Eddy et al. describes a fluorocarbon elastomer fuser member which contains cupric oxide to interact with the polymeric release agent and provide an interfacial barrier layer.
U.S. Pat. No. 5,464,698 to Chen et al. describes fuser rollers having a surface layer comprising fluorocarbon elastomer and tin oxide fillers. The fillers provide active sites for reacting the mercapto-functional polydimethylsiloxane.
Fuser members of condensation-crosslinked PDMS elastomers filled with metal oxides are disclosed, for example, in U.S. Pat. No. 5,401,570 to Heeks et al. This patent describes a silicone rubber fuser member containing aluminum oxide fillers which react with a silicone hydride release oil.
U.S. Pat. No. 5,480,724 to Fitzgerald et al. discloses tin oxide fillers which decrease fatigue and creep (or compression) of the PDMS rubber during continuous high temperature and high stress (i.e. pressure) conditions.
Some metal oxide filled condensation-cured PDMS elastomers are also disclosed in U.S. Pat. No. 5,269,740 to Fitzgerald et al. (cupric oxide filler), U.S. Pat. No. 5,292,606 to Fitzgerald (zinc oxide filler), U.S. Pat. No. 5,292,562 to Fitzgerald et al. (chromium oxide filler), and U.S. Pat. No. 5,336,596 to Bronstein et al. (nickel oxide filler). All provide good results.
However, it is conventionally known in the art that fillers useful in one elastomer material may not be useful in a different elastomer due to chemical or other interactions that may differ substantially between material types. Different metal and non-metal oxides also may behave differently and be unsuitable for use in a fuser member.
U.S. Pat. No. 4,264,181 to Lentz et al. includes lead oxide as a suitable filler in various fluorocarbon elastomers (Viton E430, VitonE60C, Viton GH), yet U.S. Pat. No. 5,017,432 to Eddy et al. teaches that lead oxide is undesirable on the basis that it produces an unacceptable fuser member with similar fluorocarbon elastomers (Viton GF).
U.S. Pat. No. 4,515,884 to Field et al. discloses a fuser member which utilizes metal oxide filled polydimethylsiloxane. The metal oxides are iron and tabular alumina, while calcined alumina is described as being unsuitable for use.
U.S. Pat. No. 4,562,335 to Katsuno et al. discloses a silicon carbide filled condensation-cured PDMS elastomer providing good release.
U.S. Pat. No. 4,763,158 to Nitzsche describes boron nitride as a useful filler in polydimethylsiloxane elastomers; however the results it achieves indicate that in fluorocarbon elastomers it demonstrates poor release performance and is unsuitable for use.
U.S. Pat. No. 3,050,490 to Nitzsche et al. disclose the use of boron nitride fillers in silicone elastomers to control the degree of self-adhesion of the vulcanized silicone rubber. The compositions are described as being useful for applications for self-adhering silicone rubber such as electrical insulating, joint sealants, packing rings, laminating materials, etc.
U.S. Pat. No. 4,292,225 to Theodore et al. discloses a thick highly filled thermally conductive elastomer which comprises an organopolysiloxane with a viscosity modifier, silica and a thermally conductive boron refractory powder preferably boron nitride which aids thermal conductivity. These highly filled thermally conductive elastomers are described as being useful in ring gear assemblies.
Unfortunately, as fuser rollers wear, the fillers that are exposed react not only with the functionalized polymeric release agent, but also with the toner, paper substrate, and charge control agent. Such reactions build up debris on the surface of the fuser roller, causing deterioration of toner release and great reduction in the life of the fuser roller.
Thus, there remains a need for fuser members whose fillers have a low propensity to react with toners or are made to enhance the interaction between the elastomer and filler and also between the polymeric release agent and filler. In particular, there remains the need for a unique combination of fluoroelastomer, non-metal oxide and curative system which overcomes or at least minimizes the above deficiencies.
The present invention is directed to overcoming the problem encountered in the art.
The present invention relates to an electrophotographic system, which has a member with a surface layer and also may include a base layer. The surface layer is prepared from a surface layer composition, including a fluoroelastomer and a boron nitride filler coupled with a silane.
The present invention also relates to a thermally conductive fuser member with a surface layer over a base layer. The surface layer is prepared from a surface layer composition, including a fluoroelastomer and a boron nitride coupled with a silane.
The present invention provides an effective way to solve the problems described above. For example, by filling a fluorocarbon elastomer with boron nitride filler particles treated with a coupling agent, such as a silane, the present invention provides a fuser member with the desired thermal conductivity and may have improved wear properties.
An additional advantage is that the present invention allows for a high percentage of boron nitride fillers in the fluorocarbon elastomer and therefore high thermal conductivity can be achieved. In conjunction with high filler loadings, boron nitride has the added advantage of low density and reduced tendency for the filler to drop out during solvent coating.